Electrical signal amplifying and repeating system



y 2, 1929- B. F. MIESSNER I 1.719.189- I v- ELECTRICAL SIGNAL AMPLIFYiNGAND REPEATING SYSTEM I 1 FiledAug. ir, 1925 Patented July 2, 1929.

UNITED s rATEs'PArrNT OFFICE.

BENJAMIN MIESSNEB, F SOUTB ORANGEQNEW JERSEY.

' ELECTRICAL SIGNAL AMPLIEYING AND REPEATING SYSTEM.

Application filed August 17, 1925. Serial No. 50,555.

"the amplifying and repeating devices to render them operative,particularly where other than steady sources of potential are 7 used forenergizing the filament and plate circuits of three-electrode vacuumtubes. I have particularly in mind the use of alternating currents fromordinary house-lighting circuits as the energizing source.

This invention constitutes an improvement over that described in myco-pending application Serial No. 29,859 of May 13, 1925, in which Isystem for amplifying and repeatingelectrical signals wherein aplurality of threeelectrode vacuum tubes were energized from a source ofalternating current, together with means and procedure for eliminatingthe bum that usually results from. the use of such currents. I havefound that substantialimprovement is obtained by certain furtherprocedure with properly chosen and co-ordinatcd apparatus, which furtherimprovements are the subject of my present invention.

My invention will be best understood by reference to the figure in theaccompanying drawing which illustratesdiagrammatically a; complete radioreceiver employing fivein vacuum tubes whose plate and filament circuitsare energized from a source of alternating current. as hereinafter morefully described. VT

and ,VT" indicate two tubes arranged for AA radio frequencyamplification, VT indicates a detector tube. and VT and VT indicate twotubes arranged for a'udiofrequency amplification. The plate circuits ofthese tubes are energized by unsteady direct current derived fromrectifying and filtering preferably cycle alternating current, thearrangement comprising anordinary lamp plug LP connecting the primary ofa power transformer PT through a switch S and an 55 indicating lamp andsafetl fuse L to the source of supply. An ordinary three-elece receptionof radio signals wherein three-- rectifying tube. A

illustrated and described a tor action is a little with means foreliminating hum trode vacuum tube VT is converted in effect into atwo-electrode tube for rectification purposes by connecting the grid andplate elements together as shpwn. A secondary winding S energizes thefilament of the secondary winding S provides the currents to berectified vacuum tube VT and filtered by the combination comprising thetwo parallel con-- densers C and C and the series resistance by the R,preferably made variable for proper control of the energy supply to theplate circuits of the operating vacuum tubes. The resistances R and Rdivide the rectified and filtered energy into two potentials, oneusually l'llglLfOI the amplifiertubesof the system, and supplied theretoby the line B, and one usually low for the detector tube of the system,and supplied thereto by the line' B". The line PR "provides a platereturn for connection to the several filaments.

The secondary winding S and lines AA supply unrectified alternatingcurrent for heating the filaments of the first four vacuum tubes of thesystem. The extension secondary windings S S and the lines A i A supplyunrectified alternating current VT loud speaker LS, and is a morepowerful tube than the preceding ones. Good deteccur'rent adjustmentthan amplifier tube action, so that the filament circuit of detectortube VT- includes a current control resistance R. i a

The grids of all of the vacuum tubes are connected to a GR, which lineincludes a grid biasing battery CB and which is connected to thefilaments through-a variable contact X associated with a connectedacross the filament supply lines fier VT 'through the action of variablecondenser VC and variable inductance or variometer VL. The amplifiedhigh frequency currents are selectively transferred from tube VT to tubeVT through radio frequency transformer with the assistance of variablecondenser V0 The high fremore critical to filament common grid returnvor line resistance or potentiometer includes a variable inductance orvariometer VL to permit of adjusting the coupling for best results withvariation of frequency of received radio signals. The detected currentsare assed to vacuum tube VT through an io frequency transformer AF,

1 which transformer has a high resistance R in shunt to its secondarywinding for the purpose of lessening its tendency to assist roduction ofoscillations in the system. The audio frequency amplified currents arepassed from "vacuum tubeVT to vacuum tube VT through association of thelower half of the primary winding of audio frequency transformer AF withthe secondary winding of this transformer. fre uency currents, finallyhighly amplified in t s more powerful tube amplifier VT are convertedinto wund in the loud speaker An arrangement is shown whereby the audiofrequency currents can be stopped short of the vacuum tube VT anddirected instead into head telephones HT. vit will be seen that when thetelephone plug TP is inserted in the telephone jack J, the headtelephones are connected directly across'the secondary winding of audiofrequency transformer AF through the plugmalring contact with the lever1 connected to one side of the secondar winding and through the jackconnecte to the other side of the secondary winding. Also that levers i,2, 3 and t cooperate to open the filament circuit and the rid circuit ofvacuum tube Vl It is very important to open up the grid circuit ofvacuum tubefVT and tie-energize the tube when the telephones areconnected to the first stage of audio frequency amplification because,if left connected and energized, stray fields from the alternatingcurrent system in the receiver will be picked up by the circuits ofthislast and free tube and amplified to create considerable annoyance fromthe loud speaker.

With the plate and filament circuits of the tubes energized-with theform of unsteady current shown at least three sources for hum exist asfollows: (1) the impure currents resulting from rectification andfiltration supplie to the plate circuits; (2}, the nlternating currentsupply for heating the filaments periodically varies the potentialacross the terminals of the filainents alternately positive andnegative, and, since the grids must be connected tosome point of thefilament, there results a varying potential upon the grids; and (3), thetemperatures of the filaments vary somewhat in consonance with thealternating currents heating the filament, resulting in a varvingcreating annoying The audio electron emission by the'filaments at doublethe frequency of the alternating currents. Since the usual frequency ofavailable alternating current supply is 60 per second, it will be seenthat the disturbing currents resulting from the conditions I haveoutlined above are of an extremely low frequency compared to the radiofrequency signal currents handledby the radio frequency portion of myreceiver, and are also low in frequency compared to the great majorityof signal currents handled in the audio frequency portion of myreceiver. Very little or no difficulty therefore arises in vacuum tubesVT and VT and their associated circuits because the radio frequencytransformers which convey the currents through and beyond these tubespass to a negligible degree the disturbing currents. The trouble heginsin the detector tube VT where the audio frequency transformer AF more orless efficiently passes forward disturbances arising in this tube. Thesedisturbances are subject to double amplification in vacuum tubes VT andVT; Similarly, disturbances arising in vacuum tube Vl are more or lessefficiently assed on to vacuum tube VT and amplifie It will be seen thatdisturbances arising in vacuum tube VT, the last tube, are not subject'to further amplification, and may, under proper conditions, not becomepractically annoying.

It will be seen that I provide in the output circuit of my radiofrequency amplifier tube V T a high frequency path through the variableinductance VL forming the primary of radio frequenc transformer RF", andcondenser C an a low frequency path through the upper half of theprimary of audio frequency transformer AF? The result is that highfrequency signal currents passing through this tube continue on inregular manner to the detector tube, while low frequency currentsresulting from the disturbing conditions I have outlined act on audiofrequency transformer AFR lly muking the windings of the primary of AFoposite in action, disturbing currents arising in VT are made to opposedisturbing currents arising in or conveyed by VT, thereby neutralizingdisturbing currents without neutralizing low frequency signal currentsbecause no appreciably low frequency signal currents exist in the u perhalf of the winding. Such a system have fully described in my co-pcndingapplication 29.- 859 of May 13, 1925, together with how such a svsternmight be extended to provide ncutralization of disturbin currentsarising in the lust tube, if neutralization to a high degree is desired.It is readily apparent that with the radio receiver shown, vacuum tubeVT is available for neutralizing effect on vacuum tube VT in the samemanner that neutralization is carried out between vacuum tube VT and VT.It is, of course,not necessary that the neutralizing tubes be a part ofthe radio receiving system. Separate tubes could be emplo ed in themanner described and illustrated cedure. would be an unnecessaryduplication of material where the radio frequency tubes in a system suchasI have shown are available and can be made to serve the dual capacity.

Existing types of vacuum tubes have rarrived at designs of filamentsbest suited to operation from batter sources of energy. Batteryconstruction, ife and maintenance compel developing the necessaryfilament power consumption through small current supplied at acorrespondingly high voltage. The ratio of voltage to current has so farnot been less than 5 to 1. The demand for low current has furtherbrought about the use of filaments of small diameter and small mass,operated at extremely high "temperatures for high rates of electronemission, resulting in an arrangement of very low temperature inertia,and therefore most susceptible to varying electron emission when heatedby alternating currents. The high voltage across the filaments ofexisting tubes is most undesirable for alternating current a heating,because the wide variation in potential across the filament increasesthe tendency to impress a varying potential on the grid through itsnecessary connection to the filament, It is customary, in trying to minimize theefl'ect on the grid, to connect the grid return. to atheoretical mid-point of a potentiometer connected across the filamentsupply line, or to a theoretical mid-point or center tap of the filamenttransformer secondary winding. At best, the mid-point connection is onlytheoretical, and it is readily apparent that the greater the totaldifference of potential across the filament, the greater Wlll be thedisturbance arising from an imperfect mid-point connection.

It is readily appreciated that in supplying filament current through analternating current transformer, it makes no substantial differenceinthe source of supply how large the current may be in order to reach alow voltage characteristic desirable for alternat' ing currentoperation. For instance, a pres! ent efficient vacuum tube requiresapproximately 1 watts in the filament supplied at about 6 volts with fl;ampere of current: I findthat a similar vacuum tube having this powerconsumption in the filament supplied at 1 volt and 1 amperes of currentis much more desirable in characteristics for use in an alternatingcurrent energized system. Such a tube would necessarily have a muchlarger diameter filament than now in use, thereby increasing its massand increasing its heat inertia. Also in viewofthe availability of largecurrents in alternating opbut such pro-i oration, the filament could befurther in;

creased to obtain larger surface for'lower temperature operation withoutsacrificing total electron emission, thus still further increaslng thedesirable heat inertia characteristic.

the first our vacuum tubes have the low voltage and high inertiatemperature fila-- to towards complete hum elimination, and

my presentinvention refers particularly to a system embodying this addedfeature.

In the stem shown and described by me It will therefore be seen that theuse of alternating current for heating filaments lends itselfparticularly well to using tubes having different filamentcharacteristics inthe same system. For instance, by extendin secondarywinding S somewhat on each si e to include the additions S" and 8", I amenabled to use the more powerful vacu um tube VT in the last stage foroperating a loud speaker, the filament voltage for this tube beingconsiderably higher than for the other tubes.

While I depend for hum elimination to a large extent upon theneutralizing arrange ment and the use of low voltage and high heatinertia filaments, I have introduced another factor which I find ofparticular value in eliminatin the disturbance in the last and unneutraized stage of' audio. frequency amplification. It will be seen that Iprovide a variable contact X for the gridreturns of the vacuum tubes tothe potenti 'ometer R across the filament supply circuit.

Considering now the audiofrequency transformer AF, ifthere is a completebalance of the disturbing currents in the two halves of the primarywinding so that no disturb ing currents are transferred to the vacuumtube VT, there will be nothing to neutralize the disturbing currentsarising in this tube. However, if disturbing currents should beintroduced into the grid circuit of this tube out of phase with thosearising in the tube, they, may be utilized for new tralization. Byvarying the contact X from one side to the other of the theoreticalmidpoint of the potentiometer R I amenabled cause,of amplification,capable of effectively opposing the greater intensity of disturb ancesof the high voltage filament of the power tube of the last stage.

\Vhile I have utilized a radio receiver for the purpose of illustratingand describing trodes, means for impressing the alternating currents tobeamplified upon said system,

means for passing the amplified currents from one tube to anotherincluding connections between the grids and filaments of said tubes,means for operatively energizing said -tubes including means for heatingthe filaments of said tubes from un' steady sources of. potential, thefilaments of said tubesbeing adapted to consume energy for heating at arate determined by a predominant currentcomponent, means for uniformlydistributing the potential and phase variations in said filament heatingsystem due to .said unsteady currents, and means connecting said gridsto such a point of said distributed potential and phase as to i causevariations of potential to be impressed vacuum tube on said grids insuch a manneras to neutralize variations in the amplified plate currentin the last of said tubes caused by the unsteady, filament heatingcurrents.

. 2. A system including three-electrode amplifiers of alternatingmm-rents having grid, filament and plate electrodes, means forimpressing the alternating currents to be amplified upon said system,means for passing the amplified currents from one tube to .anotherincluding connections between thegridsand filaments of said tubes, meansfor operatively energizing said tubes including atransformer ments, thefilaments of said tubes being supplying alternating current, to saidfilaadapted to consume energy for heating at a rate determined by apredominant current Icomponenh-means for uniformly distributmg thepotentialand phase variations in said filament energizing system due tosaid alternating currents, and means connecting said grids to such "apoint of saiddistributed potential'and phase as to cause variations ofpotential to be impressed on said grids in such a manner as toneutralize variations in the amplified plate'current in thelast of saidtubes caused by'the unsteady filament heating currents. I

3. In an electrical amplifying system,-a plurality of vacuum tubes, eachhaving a plate, filament and grid, circuits for supplying alternatingheating current to different .mary an filaments at different potentials,said circuits having a common point which is substantially neutral toeach of said circuits, a connection between each of said grids and saidpoint, a single source of potential, and plate circuits connected tosaid source, said circuits including a connection from said source tosaid point.

4. Means for supplying alternating current at different voltages to thefilaments of different three-electrode vacuum tubes of an amplifyingsystem and for providing a connection between the grid circuits of thetubes and the filament supply system, said means consistin of atransformer having a pria secondary winding, a pair of filamentsupplytaps connected to intermediate points of. the secondary winding atopposite sidesof the neutral point of the secondary winding, animpedance connected across the taps and a grid-connection tap connectedto an intermediate point of said impedance. I

5. Means for supplying alternating current at dificrent voltages to thefilaments of different three-electrode vacuum tubes of an amplifyingsystem and for providing a connection between the grid circuits of tubesand the filament supply system, said means consisting of a transformerhaving a pri mary and a secondary winding, a pair of filament supplytaps connected to intermediate points of the secondary winding at opposite sides of the neutral point of the secondary winding, a resistanceconnected across said taps and a grid-connection tap adjustable todifferent points of said resistance.

6. A system including three-electrode vacuum tube amplifiers ofalternating currents, having grid, filament and plate electrodes, meansfor impressing the alternating currents to be amplified upon saidsystem, means for passing the amplified currents from one tube toanother including connections between the grids and filaments of saidtubes, means for operatively energizing said tubes including means forheating the filaments of said tubes from an unsteady source ofpotential, the filaments of said tubes being adapted to consume energyfor heating at a low operating temperature at a rate determined by apredominant current component, means for uniformly distributing thepotential-and phase variations in said filament heating system due to.said unsteady currents, and means connectingsaid grids to such "a pointof said distributed potential andphase as to cause variations ofpotential to be impressed on said grids in such a manner as toneutralize variations in the amplified plate current in the last of saidtubes caused by the unsteady filament heating currents.

7. The system as claimed in claim 1 wherein a transformer is provided,which transformer has a secondary winding from which are supplied. thecurrents for heating the filaments at different voltages and whereinconnections are rovided for supplying the higher or big est voltage fromthe secondary winding and for supplying the lower voltage or voltagesfrom a central section or central sections of the secondary Winding.

8. In a signal current amplifying system a plurality of three-electrodevacuum tubes arranged for multi-stage amplification of signalingcurrent, the filaments of one or more of the tubes in advance ofthe lasttube being massive and heated by current of relatively low voltage andthe filament of the last tube bein ada ted for heating by current ofrelatively hig voltage, means for energizing said'filaments from a com-irnon source of alternating current energy whereby periodic disturbingvariations are created in the plate circuits of said tubes, and meansfor passing to the grid circuit of the last tube some of the disturbingenergy of a preceding tube of phase after amplification to oppose thedisturbing energy-in the plate circuit of the lastltube.

9.. In a signal current amplifying system a plurality of three-electrodevacuum'tubes arranged for multi-stage amplification of signallingcurrent, the filaments of one or more of said tubes being massive andheated by large current: at low voltage and the filament of another,tube being ada ted to be heated by current at relatively h1ghervolt-'age, means for heating all of said filaments from a common sourceofalternating current, whereby disturbin' g periodic variations areproduced in the p ate circuits of said I tubes, and means for passing tothe grid cir-e ergy in the plate circuit of said higher voltone of saidtubes having a cathode producing relatively large disturbing variationsin tllll .llllh its pte circuit when energized by alternat ing current,means for ener izing the cathodes of all of said tubes rom a commonalternating current source, and means for passing to the grid circuit ofsaid tube havmg relatively large disturbing variations some of thedisturbing energy in the plate circuits of the other of said tubes ofphase utter amplification to oppose energy in the pose disturbing energyplate circuitof said tube having relatively large disturbing variations.

11. A signal current amplifying system including a pair ofthree-electrode vacuum tubes connected in cascade relation, one of saidtubes having a cathode producing relatively small and the other of saidtubes having a cathode producing relatively large disturbingvariationswhen energized with periodically fluctuating current, means forenergizing the cathodes of both of said tubes, from a common source ofperiodically fluctuating current, said tubes being so associated in saidsystem that the disturbing energy of the first of'said tubes isintroduced into. the grid circuit of the second of said tubes in a phaseto oppose the disturbing energy in the plate circuit of the second saidtube. R R,

12. In a cascade system for amplifying signal current of high frequencymodulated at audible frequency including a three-electrode vacuumfunctioning as a detector followed by one or more three-electrodevacuum, tubes functioning as audio amplifiers, means for energizing theoathodes-of all of said tubes from a common source of audible frequencyperiodically fluctuating current, the cathode of said de-,

tector tube producing relatively small disturbingvariations by reason ofsaid fluctuat- 'current energizing and the cathode of a relativelylarger disturbing variations by reason of said fluctuating currentenergizing, and means for introducing some of the disturbing energy ofsaid detector tube into the grid circuit of said following tube of phaseafter amplification to efi'ectivcl o)- ose the distur ing variationsjnsaicl fdl owing tube.

13. In a system for amplifying and translating signal current thecombination of a loud-speaking translatin electrode vacuum tube ofsubstantial power for operating said translating device, said withalternating current produces substantial disturbin current variations inthe plate circuit thereof, one or more less powerful amplifying tubespreceding said output tube havin cathodes which when ener ized withaternating current produce atively small disturbing current variationsin the plate circuits thereof, means for ,energizing the cathodes of allof said tubes. from a common source of alternating device, athree- 1nfollowing audio amplifier" tube producing tube having a cathode whichwhen energized current, and means for passing to the grid circuitof'said'power tube someof the disturbing energy of saidpreceding tube ortubes of phase after amplification to opin the plate circuit of saidoutputtube.

In testimony whereof I affix my signature.

BENJAMIN F. MIESSNER.

